1. Field of the Invention
The present invention relates to an electron gun for a cathode ray tube, and more particularly, to an electrode unit having improved electron beam passing holes for forming a quadrupole electronic lens of an electron gun and an electron gun for a cathode ray tube using the same.
2. Description of the Related Art
In general, a color cathode ray tube deflects an electron beam emitted from an electron gun by a deflection yoke in accordance with picture signals and lands the electron beam on a fluorescent screen, thereby forming a picture image. In order to obtain a cleaner picture image, it is important to land the electron beam emitted from the electron gun on an exact landing position of the fluorescent screen.
However, in the electron beam emitted from the electron gun and landing on the periphery of a screen after being deflected by the deflection yoke, the size of the beam spot becomes larger and the shape of the beam spot is distorted due to a non-uniform deflection magnetic field and a geometric curvature of a screen surface, which adversely affect, in particular, the resolution of a television necessitating a high definition such as a HDTV or a wide-vision television.
To overcome such problems, a dynamic focusing electron gun using a quadrupole lens has been employed, in which the shape of an electron beam is deformed in advance and focal lengths of the electron beam when it lands on the center and periphery of the screen are made different. In order to form the quadrupole lens, a dynamic voltage synchronized with a deflection signal and a focus voltage are applied to a plurality of electrodes on which electron beam passing holes are formed, or two dynamic focus voltages and two focus voltages are applied thereto, respectively.
FIG. 1 shows an example of electrodes forming the quadrupole lens.
As shown in the drawing, a vertically elongated electron beam passing hole 11h is formed on a first electrode 11, and a horizontally elongated electron beam passing hole 12h is formed on a second electrode 12 which is disposed opposite to the first electrode 11. A predetermined focus voltage is applied to the first electrode 11, and a dynamic focus voltage synchronized with a deflection signal produced when an electron beam is deflected toward the periphery of the screen is applied to the second electrode 12.
Since the first and second electrodes 11 and 12 forming the above-described quadrupole lens have the electron beam passing holes 11h and 12h elongated vertically and horizontally, respectively, the electron beam passing through the quadrupole lens converges horizontally and diverges vertically so that its cross section becomes vertically elongated. Thus, the distortion of the electron beam, which is formed by a Lorentz force when the electron beam passes through a non-uniform magnetic field formed by a deflection yoke, and the distortion of the electron beam of the periphery of the phosphor screen can be compensated for.
However, the electrodes forming the quadrupole lens cannot satisfactorily compensate for the cross sectional distortion of the electron beam landing at the corners of the phosphor screen . In other words, even if the cross section of the electron beam is vertically elongated, since the electron beam deflected diagonally with respect to the screen lands at the corners of the screen, the cross sectional distortion of the electron beam cannot be completely compensated for.
To solve the above problems, it is an objective of the present invention to provide an electrode unit which can prevent cross sectional distortion of electron beams landing throughout the screen and enhance the resolution of a cathode ray tube by improving focus characteristics of the electron beams, and an electron gun for a color cathode ray tube employing the electrode unit.
Accordingly, to achieve the above objective, there is provided an electrode unit for forming a quadrupole lens including a first electrode having three first-elongated electron beam passing holes slanting in one direction at a predetermined angle with respect to the longitudinal axis, and a second electrode having three second-elongated electron beam passing holes slanting in a direction opposite to that of the first-elongated electron beam passing holes at a predetermined angle with respect to the longitudinal axis.
Also, there is provided an electron gun for a color cathode ray tube including a triode consisting of a cathode, a control electrode and a screen electrode, and first and second focus electrodes facing each other and installed sequentially from the triode, for forming quadrupole lenses for focusing and accelerating an electron beam emitted from the triode, wherein three first-elongated electron beam passing holes slanting in one direction at a predetermined angle with respect to the longitudinal axis are formed on the facing surface of the first focus electrode, and three second-elongated electron beam passing holes slanting in a direction opposite to that of the first-elongated electron beam passing holes at a predetermined angle with respect to the longitudinal axis are formed on the facing surface of the second focus electrode, and wherein a dynamic focus voltage synchronized with a deflection signal is applied to the first focus electrode and a focus voltage is applied to the second focus electrode.
According to another aspect of the present invention, there is provided an electron gun for a color cathode ray tube including a triode consisting of a cathode, a control electrode and a screen electrode, a pair of first focus electrodes facing each other for forming a first quadrupole lens for focusing and accelerating an electron beam emitted from the triode, and a pair of second focus electrode facing each other for forming a second quadrupole lens for focusing and accelerating an electron beam having passed through the first quadrupole lens, wherein three first-elongated electron beam passing holes slanting in one direction at a predetermined angle with respect to the longitudinal axis are formed on the facing surface of one of the first focus electrodes, three second-elongated electron beam passing holes slanting in a direction opposite to that of the first-elongated electron beam passing holes at a predetermined angle with respect to the longitudinal axis are formed on the facing surface of the other of the first focus electrodes, and wherein a vertically elongated electron beam passing hole is formed on the facing surface of one of the second focus electrodes and a horizontally elongated electron beam passing hole is formed on the facing surface of the other of the second focus electrodes.